A Systems Perspective on Electrification and the Replacement of Fossil Fuel Energy

Version 2, revised March 14, 2022

Replacement of the Burning of Fossil Fuels for Generating Energy

• Humanity has to cut back drastically on the burning of fossil fuels (coal, natural gas, and petroleum) to generate energy, in order to prevent disastrous climate change and other adverse effects.
• Energy production needs to transition to means that do not produce and release greenhouse gases such as carbon dioxide, nitrous oxide, and methane.
• The transition needs to be worldwide. Simply reducing fossil fuel burning in one geographic region while continuing in another geographic region will have little benefit, since the atmosphere is connected planet-wide.
• The energy system needs to consider all aspects: the primary production of energy, the distribution of energy from where it is produced to where it is used, and the consumption of energy at the end point.
• It is critical to take the longest-term perspective possible. What can we do that will be sustainable over many human generations—ideally, hundreds or even thousands of generations?

Electrification

• The primary path forward is to replace fossil fuel-based energy systems with systems that produce, distribute, and transform energy in the form of electrical power.
• Where energy systems employ steps that are not electrical in nature, these steps must avoid emitting greenhouse gases or other significant environmental pollutants.

Improvement in Energy Use Efficiency

• The current use of fossil fuels to produce energy is very inefficient. For example, the chain from the energy content of petroleum in the ground to the energy content of an automobile burning gasoline on the highway has large losses at every intermediate step. The required transformation is going to require that every step be made as efficient as possible and all energy losses have to be cut to an absolute minimum.

Renewable Energy Sources That Do Not Produce Greenhouse Gases

• There are in fact only a few primary sources of energy that are effectively inexhaustible. One is the energy bathing the surface of the Earth from the sun. A second is heat coming from sources deep in the Earth, particularly produced by radioactive decay of elements in the mantle. A third is tidal forces from the gravitational influence of Earth’s moon.
• Renewable energy systems tap one of these three sources, in one way or another.
• Systems to exploit these sources tend to fall into a small number of types:
  • Solar energy systems, either photovoltaic or solar-thermal
  • Wind energy systems
  • Wave energy systems
  • Tidal energy systems
  • Hydroelectric energy systems tapping water flow in river systems
  • Geothermal energy systems
  • Ocean thermal gradient systems
• While not based on renewable energy sources, fission-based nuclear power systems do not produce greenhouse gases. However, there are many other considerations to be taken into account for use of nuclear power to replace fossil fuel power generation. Particularly important is the safe long-term disposal of radioactive waste, which can remain hazardous for centuries.
• Hydrogen fusion-based nuclear power systems are a long-term prospective solution to energy sources that do not produce greenhouse gases. The technical challenges are enormous and fusion power has had sixty years of intense work without a practical system emerging yet. However, significant progress is now being made. Fusion power could provide a long-term solution for nuclear-based high-capacity electric power generation that will not generate high-level radioactive wastes.

Energy Distribution and Conversion

• In addition to producing energy at a source location, it is typically necessary to distribute the energy to other distant locations where it is to be used for human purposes. Two primary mechanisms have dominated the transportation of energy from renewable sources:
  • Electric energy transmission via power lines
  • Non-carbon-based gaseous fuel distribution via pipelines or tank transport. Candidate gaseous fuels that do not contribute to greenhouse gas emissions themselves are hydrogen and ammonia, because they have no carbon. Burning hydrogen yields water. Burning ammonia yields water and nitrogen.
• Finally, it is necessary to do conversion of the energy distributed to its use location into either other forms of energy or into work, such as operating a motor.
  • For example, if the energy is distributed as hydrogen or ammonia, it may need to be converted back into electrical energy by a fuel cell or a combustion engine-generator set.

The Need for Energy Storage

• In most cases, the renewable energy sources have varying outputs over time. Solar energy systems don’t produce energy at night or during cloudy conditions, wind energy system outputs vary with the wind velocity, and wave energy systems are variable. A major current challenge is to provide energy storage systems that store energy produced at one time and release it for use at another time, to be able to match supply with the instantaneous demand.
• The energy storage systems can be co-located with the renewable energy production system, co-located with the energy consumption systems, or at other locations best suited to the storage mechanism used.
• As renewable, non-greenhouse gas producing systems take over more and more of the production of power for society’s needs, the capacity of energy storage systems will have to expand at a tremendous rate.
• Today, the greatest capacity of energy storage systems is in pumped hydroelectric installations. When excess electrical power is available during the day, water is pumped up to a reservoir at a high elevation. When more electrical power is required than is being produced by renewable energy systems, the water is allowed to flow through power-generation turbines into a reservoir at a low elevation.
• The key consideration for any energy storage system is the end-to-end efficiency of the system (i.e., how much energy is lost in the process from energy input to energy output).
• Somewhat similar to pumped hydroelectric systems are pumped air systems. When excess electrical power is available, air is pumped into sealed underground reservoirs (typically large caverns), to be released through air turbine generator systems when power is needed.
• Both pumped hydroelectric and pumped air energy storage systems depend on special geographic/geologic features (elevation differences and sealable underground caverns).
• Electrochemical cell batteries are an obvious approach for energy storage. However, the amount of energy that can be stored in a battery practically is limited due to the low amount of energy stored per unit volume and their high cost per kilowatt-hour stored.
• Storage of energy in the form of hydrogen or ammonia is a possible approach that is scalable to very high capacity. The hydrogen can be produced by electrolysis of water using renewable energy to power the electrolysis. At the other end, the hydrogen can be converted to electrical energy using a hydrogen fuel cell that produced water as the output. Alternatively, the hydrogen can be used in a combustion engine-generator set, again producing water as the output.
• A number of mechanisms are being investigated using the storage of gravity-based potential energy. One interesting option takes advantage of unused vertical mine shafts. A heavy weight is raised by the motor part of an electric motor-generator set when surplus power is available. The weight is lowered when power is needed, driving the generator part. Another version of this uses heavy rail cars on a steep section of rail. The cars are raised up the slope when surplus power is available and lowered down the slope when power is needed.
• Super flywheels are being investigated for the storage of rotational kinetic energy. The flywheels are spun up using the motor part of a motor-generator set when surplus power is available and the kinetic energy is extracted by the generator part when power is needed.
• Another means of energy storage is based on thermal energy. A large mass of material with high heat capacity (such as a molten salt) is heated when surplus power is available. Then the heat is extracted by a conversion system when power is needed. A wide range of closed-cycle mechanisms for thermal energy extraction are available, for example a steam turbine.

Electric Grid Interconnection

• Most of the renewable electric energy sources (solar, wind, wave, tidal, etc.) vary in the amount of energy produced as a function of time of day, season, etc. However, the sources are somewhat independent. For example, wind energy may still be produced while solar energy production has ceased at the end of the day. Also, different geographic regions may produce power from each source at different times. Interconnecting renewable sources together on a continent-wide scale will provide a number of benefits.

Other Needed Actions for Avoiding the Release of Greenhouse Gases

• In addition to stopping the burning of fossil fuels, another critical step is greatly reducing the release of greenhouse gases from other human actions. For example, methane is released from tens of thousands of abandoned natural gas wells and leaks in natural gas distribution systems, as well as being flared from producing oil wells.
• Chlorofluorocarbon refrigerants are extremely potent greenhouse gases. It is critical that we quickly move away from using these environmentally destructive gases in air conditioners, heat pumps, refrigeration systems, and many other chemical processes. Existing systems using these gases must be managed so that the gases are not released during servicing and disposal of the systems.
• Livestock, particularly cattle, are major producers of methane. Humans need to move away from the huge amounts of land and water resources used for raising livestock, as well as reducing the number of animals themselves.
• The current technology used for producing cement is a major source of the release of carbon dioxide. New technology greatly reduces or eliminates this source of greenhouse gas emissions.
• The production of fertilizer is another major source of the release of greenhouse gases. Alternate technologies need to be adopted to reduce this source.